Plants, fungi and bacteria synthesize the amino acids valine, leucine and isoleucine via a common pathway. One of the enzymes in this pathway is acetolactate synthase (ALS) (otherwise known as acetohydroxyacid synthase or AHAS), which converts pyruvate into 2-acetolactate as the first step in the synthesis of valine and leucine, and also converts pyruvate and 2-ketobutyrate into 2-aceto-2-hydroxybutyrate, the precursor of isoleucine. The activity of wild-type acetolactate synthase is sensitive to the action of several known classes of toxic compounds, including sulphonylurea and imidazolinone compounds. As such, such toxic compounds may be employed to kill cells containing acetolactate synthase proteins that are sensitive to those compounds.
This disclosure relates to acetolactate synthase enzymes that provide resistance to toxic compounds, and hence are useful selectable markers for recombinant cells.